1. Field of the Invention
This disclosure relates generally to providing redundancy support for network devices. More particularly but not exclusively, the present disclosure relates to providing redundancy support for network address translation (NAT) devices (such as routers or switches) in the event of a failover.
2. Description of the Related Art
Network address translation (NAT) is the translation of an Internet Protocol (IP) address used within one network to a different IP address known within another network. One network is designated as the inside network and the other network is designated as the outside network.
Generally, a company maps its local inside network addresses to one or more global outside IP addresses, and unmaps the global IP addresses on incoming packets back into local IP addresses. This provides a form of security since each outgoing or incoming request must go through a translation process that also offers the opportunity to qualify or authenticate the request or to match it to previous request. Furthermore, the translation processes provides added security in that the internal local IP addresses are kept hidden from outsiders. NAT also conserves on the number of global IP addresses that a company needs, and lets the company use a single (or a few) global IP address in its communication with outsiders.
NAT is typically included as part of a router or other network device, which in turn may form part of a firewall. System administrators create NAT tables that perform the global-to-local and local-to-global IP address mapping. NAT can be statically defined or can be configured to dynamically translate to and from a pool of IP addresses.
Despite the advantages provided by NAT, it nevertheless is prone to problems that typically plague networks. For example, failure (which may be caused by power outages, device malfunction, viruses, etc.) will always occur despite system administrators' best efforts to guard against them. When a failure occurs, NAT is unable to perform address translation and to forward traffic. This down time will continue until the current NAT device (or some other network device that caused the failover) is repaired to bring it back online. In situations where the network may have a backup NAT device, the backup NAT device can be brought online to allow new network traffic to resume—unfortunately, there will still be some downtime and lost traffic (from current connections that were broken at the time of the failover) between the time that the failover occurs and the time that the backup NAT device is brought online.
Failure can also affect transparent cache switching (TCS) functionality. With TCS, commonly accessed web pages are cached so that the requesting client need not access the Internet each time a commonly accessed web page is desired. Instead, the client can access the cached version, thereby reducing latency and bandwidth usage associated with connecting to the Internet. In the event of a failover, the TCS device(s) are unable to provide the client with access to the cache, thus forcing the client to connect to the Internet, if such a connection is even available during the failover. Thus, with TCS systems, a failover can cause latency, downtime, and lost traffic as well.